The present invention relates generally to the field of presses that include rollers, and, in its most preferred embodiments, to the field of methods and apparatus for applying pressure to rotary cutting dies.
Presses with rollers are well known and widely used. More particularly, well known and used are presses that include a die cutting station comprising a rotary cutting die that is adjacent to a rotary anvil. A nip is defined between the rotary cutting die and the anvil, and sheet-like product is drawn through the nip while pressure is applied to the rotary cutting die to cut the product. The rotary cutting die typically includes two ends which are mounted to the press frame. Pressure is applied proximate to each of the ends of the rotary cutting die by a pair of independent roller assemblies disposed above the rotary cutting die. The roller assemblies are attached to the underside of a pressure bar proximate to the opposite ends of the pressure bar. Pressure is typically applied to the pressure bar by two independent jackscrews that function as the force applying means of the press. The jackscrews are in threaded engagement with a bridge bar that is connected to the press frame and disposed above the pressure bar. In use, the jackscrews are threaded through the bridge bar so that their shanks engage and apply force to the top side of the pressure bar. Due to difficulties in adjusting the jackscrews equally and maintaining equal loading of the jackscrews, this conventional arrangement inherently results in situations where a greater force is applied to one end of the rotary cutting die than the other. This uneven loading results in an uneven pressure distribution between the rotary cutting die and the rotary anvil.
Rotary cutting dies are typically manufactured and maintained within close tolerances in an effort to insure that they can be used to generate quality products for a long period of time. Uneven loading will typically cause a rotary cutting die to cut unevenly and wear excessively or abnormally, causing the rotary cutting die to fall outside of acceptable tolerances prematurely. Thus, there is an incentive for maintaining even loading on a rotary cutting die, and efforts have been made to maintain such even loading. These efforts have included the development of devices for independently monitoring the load applied by each jackscrew of the pair of jackscrews. By monitoring the load applied by each jackscrew individually, a user can adjust the jackscrews so that each of the jackscrews applies an equal load. However, this has its limitations because, for example, a user is required to adjust the jackscrews in an iterative manner to obtain the equal loading of the proper magnitude. Such iterative adjusting can be time consuming. Additionally, as a press operates, the parts thereof often heat up and expand such that the loading of a rotary cutting die becomes uneven to a degree that jackscrew adjustment is necessary.